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« Reply #25 on: July 13, 2015, 12:35:42 AM »
bmblb
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Clap Clap Clap
Ah, so birds can loop...
Given enough power Grin
A fine achievement. Congrats.

Thank you Iyer Sir.....

That's why I called it The Fenix ....just kidding, I was just pushing it....(the blow by blow account comes later)
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« Reply #26 on: July 13, 2015, 12:43:43 AM »
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loved the flight  Clap Clap Clap superb

thank you Sir.....it is indeed a nice feeling.

....these are hopefully my baby steps to the Grand Masters of BTP!

I meant to seek your inputs and will re post as soon as I am able to locate a pic for comparison.
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« Reply #27 on: July 13, 2015, 12:34:26 PM »
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Query:

(a)....the multicolored flying wing(MCFW) flies well (aerobatic) without the fins too, but not the Fenix despite the curved wing tips.

....If Fin gives roll stability, then the Fenix should have better roll stability due to the flattish fuselage AND the curved wingtips.

(b) The upward deflection of the elevons necessary for take off - is this really called 'reflex' or is it a case of misunderstood concept and/or misused term or both?

any/all comments welcome !


IMG_0205.jpg
Re: Fenix - 48 in KFm2 bird like plane - 2015 Sweepstakes entry
* IMG_0205.jpg (37.32 KB, 800x533 - viewed 484 times.)
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« Reply #28 on: July 13, 2015, 03:32:01 PM »
K K Iyer
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@bmblb,
Here's my 2 cents worth:
one is a swept wing, and the other is not.

When a swept wing, in level flight, gets yawed to the left, it slips to the right and two things happen:
1. The right wing presents, to the airflow, a larger frontal area than the left wing. The resultant higher drag produces a force counter to the original yaw.
2. The right wing sees a higher angle of attack and hence higher lift and drag both.

The result is a yaw correction to the right and roll inducement to the left.

When a swept wing, in level flight, gets banked to the left, it slips to the left.
The result is a roll correction to the right and yaw inducement to the left.

Hence sweep works like dihedral. There is a conventionally accepted thumb rule that i don't recall exactly (like 5 or 10 degree sweep equals 1 degree dihedral, that had been mentioned in a thread a few months ago, probably by Gusty sir)

(Effect of fuselage depends on whether the centre of side area is above/below/ahead of/behind the CG)

The upward deflection of the elevons for takeoff is just 'up elevator'. No connection with 'reflex'.

A reflexed airfoil is one where the camber, which is concave from below, becomes convex as it approaches the trailing edge. This has the same effect as decalage in a wing and stab layout. This may be built in, or achieved by setting the elevons in a raised position (for level flight). Up elevator for takeoff is over and above this.
(Coeff of moment being positive etc not being introduced into the discussion at this stage, as not reqd)

People with formal education on the subject, like rcpilotacro, or a recent member who is completing his aero degree, are requested to see if the above explanations are ok.
« Last Edit: July 13, 2015, 03:43:06 PM by K K Iyer » Logged
 

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« Reply #29 on: July 13, 2015, 11:47:10 PM »
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....Thanks ! better to clarify than misuse terms !

however, I was wondering on these lines.

1. The MCFW is evidently a swept back wing, yet, the BTP is not essentially a plank either - unless we use simple arithmetic to cancel out the forward and aft sweeps, leaving with a negligible sweep back - then why have such a wing at all (agreed that the birds change the sweep depending on how they want to fly - there are birds - well, most of the birds actually - whose wings' standard form for most part of their flying behaviour  is indeed sweep forward and then sweep back....of course changing in extreme dives and glides (perhaps for structural and collapsible reasons as well?)

....or do the sweeps (forward and aft) actually add up rather than negate, and is so designed ( by Him) so as to have a longer span, without compromising on the stability by virtue of the 'total sweep' ? I am just guessing here !!!

2. As regards 'reflex' which is a case of simple up elevator here, - what factors in a plane necessitate such a pronounced deflection to start with? For a layman, if the control surfaces are neutral and there's sufficient down thrust(?), it should fly level, right ?

or is it a case of insufficient 'down thrust' and needs another washer?

In other words, if I were to make the same plane fly with the elevons at neutral, then what should change in the plane? **

2.1....this should show up in the test glides as well, correct? why are the test glides flat, then? or is it that 60-70( I believe the glides are much longer) feet glide is too short to assess this?

Couple of more points on the curved wing tips and the fuse sides....maybe later.
« Last Edit: July 14, 2015, 09:58:52 AM by bmblb » Logged

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« Reply #30 on: July 14, 2015, 12:32:18 AM »
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The upward deflection of the elevons for takeoff is just 'up elevator'. No connection with 'reflex'.

A reflexed airfoil is one where the camber, which is concave from below, becomes convex as it approaches the trailing edge. This has the same effect as decalage in a wing and stab layout. This may be built in, or achieved by setting the elevons in a raised position (for level flight). Up elevator for takeoff is over and above this.
(Coeff of moment being positive etc not being introduced into the discussion at this stage, as not reqd)

.....Iyer Sir, I naturally came across and read about reflexed wing....

What I meant is exactly what you have written above!

.....note that the plane sank(no level flight here) inspite of the ele input.....however, AFTER the ele setting was set at Up ele permanently, THEN ele input resulted in a climb, otherwise level flight(EDIT: with a tendency to dive).

...it was necessary to get this sequence right....and guess it is reflex after all as the usable ele input was only after the 'over and above' ele setting.
« Last Edit: July 14, 2015, 09:19:42 AM by bmblb » Logged

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« Reply #31 on: July 14, 2015, 01:06:04 AM »
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Maiden Flights:

Launch 1: 25% throttle, 30% throws. Climbed nicely but no response to control inputs...so cut off and landed gently - insufficient throws AND no reflex, as I learnt.

Launch 2: 45% throws, and set the elevators at 5mm deflection (Up) from neutral and launched at a little more throttle....climbed nicely, but the prop came off.

Correction:

.....hate doing this as it may be perceived that facts are being twisted to suit theories rather than the other way around.

Nevertheless,.....

Here's the sequence of events - what was typed above is an oversight in excitement, as I now recall(the blow by blow account) :

Launch 1: On launching at about 25% throttle, the plane took the path of launch but did NOT climb.....instead on increasing throttle AND giving ele input, it flew ahead without noticable/ proportionate increase in alt, as though there was no ele input at all !!!....and therefore cut throttle and landed.

Launch 2: Two corrections were made. The ele setting was set at 'Up' by 5mm or so from neutral. This is visible in some parts of the video when the plane is flying level(EDIT: and without any control input - a trimmed flight). And the throws were increased - this is evident from the maneuvers.

In addition, there were a few loops where recovery was longer (the heavy breathing is mostly repeated sighs of relief  Grin) - would these recoveries be faster if the 'Up deflection' was set at more than what it now is AND with the same ele input?

....If so, then I think it resembles the definition of reflex ?



« Last Edit: July 14, 2015, 09:22:08 AM by bmblb » Logged

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« Reply #32 on: July 14, 2015, 09:29:27 AM »
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or is it a case of insufficient 'down thrust' and needs another washer?

In other words, if I were to make the same plane fly with the elevons at neutral, then what should change in the plane? **

Need inputs here ! It is possible I may be grossly incorrect with the reference of the 'thrust line' in this scenario.

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« Reply #33 on: July 14, 2015, 10:09:55 AM »
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Test Glides  Grin Grin Grin
 
 There are some gaps(Edit: meaning details intentionally omitted) in my account of the test glides. Any guesses from the recent posts/edits ?
..........
 2.1....this should show up in the test glides as well, correct? why are the test glides flat, then? or is it that 60-70( I believe the glides are much longer) feet glide is too short to assess this?
« Last Edit: July 14, 2015, 10:22:58 AM by bmblb » Logged

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« Reply #34 on: July 14, 2015, 11:13:48 AM »
K K Iyer
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@bmblb,
Now have to introduce CoM!
Will phone.
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« Reply #35 on: July 15, 2015, 11:24:55 PM »
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@bmblb,
Now have to introduce CoM!
Will phone.

.....at the end of our conversation, I had a couple of pages filled with something I will have to sit at to figure out/understand in moooore detail.

....it is not often that one finds people taking such interest...

thank you very much, Iyer Sir ! Sorry, I had a overnight travel and got back earlier this evening (and was just in time yesterday for the bus after 3 hours of flying..)
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« Reply #36 on: July 16, 2015, 12:51:16 AM »
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Hence sweep works like dihedral.

I must apologize before hand for how this sounds - the intention is NOT to sound cheeky.

......if sweep(assumed to be swept BACK) works like dihedral, then swept forward works like 'anhedral'? again, cancelling out each other?




 ..... OR.....



....does it work like a gull wing Huh?



OR



....like a polyhedral wing.....just adding the dihedral in the same direction?

...there really must be a reason for this shape of a wing !!!
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« Reply #37 on: July 16, 2015, 02:55:43 PM »
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....here's another video from Tuesday.

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« Reply #38 on: July 16, 2015, 04:07:19 PM »
ashok baijal
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Just happened to see the videos today. Don't know how I missed it earlier. Loved the way the "buzzard" fler
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« Reply #39 on: July 16, 2015, 09:56:30 PM »
K K Iyer
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Wow. Terrific!
Nothing succeeds like success!

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« Reply #40 on: July 16, 2015, 10:40:52 PM »
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"..there really must be a reason for this shape of a wing !!!"

But for some reason, not seen many wings like the Minimoa in the last 80 years...

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« Reply #41 on: August 26, 2015, 09:27:05 AM »
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ta da  Grin !

IMG_20150719_091504388.jpg
Re: Fenix - 48 in KFm2 bird like plane - 2015 Sweepstakes entry
* IMG_20150719_091504388.jpg (57.66 KB, 800x450 - viewed 439 times.)
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